T. Russomano* L. F. B. Chotgues* O. A. Lima de Sá* M. A. dos Santos* J. Ernsting** *Microgravity Laboratory-Brazil / ** King’s College London-UK *Microgravity Laboratory-Brazil / ** King’s College London-UK Intra-ocular and Venous Pressures during Head-down Tilt

Objectives 1) To determine the relationship between IOP and forehead venous pressure produced by 15 min exposures to: 0° (supine position), 17° HDT and 34° HDT 0° (supine position), 17° HDT and 34° HDT 2) To compare the results obtained with HDT with the ones found in microgravity 3) To discuss the physiological mechanisms involved in the increase of IOP and venous pressures with HDT and in microgravity

Physiology of the eye on Earth

IOP in Microgravity 1st German-Russian MIR mission 1992 : 92% IOP rise Schwartz R, Draeger J, Groenhoff S, Flade K D Ophthalmologe 1993; 90: nd German D-2 Spacelab-Mission 1993: 114% IOP rise Draeger J, Schwartz R, Groenhoff S, Stern C Ophthalmologe 1994; 91: 697-9

IOP - Parabolic Flight IOP increased 58% (19 mmHg) during parabolic flight (20 s of µG) compared to baseline values (12 mmHg) ( n =11) Mader TH et al., Am J Ophtalmol Mar 15; 115(3):347-50

Method 0° (control) 17° HDT 34° HDT 0° (recovery) 0° (control) 17° HDT 34° HDT 0° (recovery) 15 min 15 min 15 min 15 min 15 min 15 min 15 min 15 min IOP IOP IOP IOP IOP = intra-ocular pressure VP = forehead venous pressure IOP = intra-ocular pressure VP = forehead venous pressure VP VP VPVP

Material

Material

Results

Results

Results IOP Venous Pressure (mmHg) (n=8) (mmHg) (n=4) (mmHg) (n=8) (mmHg) (n=4) Mean ± SE Mean Mean ± SE Mean Supine 14.7 ± ° HDT 20.7 ± ° HDT 25.5 ± Supine 13.5 ±

Expected Forehead Venous Pressure 17° HDT = approximately 13.0 mmHg 6.0 mmHg (Hydrostatic Pressure) 7.0 mmHg (Venous Pressure) Our result: 13.0 mmHg 34° HDT = approximately 19.0 mmHg 12.0 mmHg (Hydrostatic Pressure) 7.0 mmHg (Venous Presssure) 7.0 mmHg (Venous Presssure) Our result: 19.3 mmHg

Central venous pressure in space Buckey J. C. et al, 1996

Conclusion IOP and forehead venous pressures simultaneously increased during HDT (r=0.99) regardless the angle of tilt employed and both returned to their control values in the supine position.IOP and forehead venous pressures simultaneously increased during HDT (r=0.99) regardless the angle of tilt employed and both returned to their control values in the supine position.

Future Studies Measurements of peripheral venous pressure of the forehead in microgravity should be made to clarify the mechanisms involved in the rise of IOP, which may differ from those found during HDTMeasurements of peripheral venous pressure of the forehead in microgravity should be made to clarify the mechanisms involved in the rise of IOP, which may differ from those found during HDT